R-butyl phenyl

Two hindered phosphoranylidenephosphines, ArP=PMc3 [76 Ar = 2,6-dimesityl-phenyl and 2,4,6-tri(r-butyl)phenyl], have been prepared and are stable in the absence of air and water. As the resonance suggests, they can enter into phospha-Wittig reactions to produce phosphaalkenes (77). The reaction gave high yields of ( )-(77) in a few hours for a range of benzaldehydes (p-Cl/N02/0Me/NMe2/H, F5), and also for ferrocenecarboxaldehyde and pivaldehyde, but was unsuccessful for ketones. 

Mixtures of R3Sn+ compounds (R= -butyl. phenyl, cyclohexyl) were separated by ion exchange-high performance liquid chromatography-graphite furnace atomic absorption spectrometry [252], The small spread in calibration slopes in Fig. 4.10 signifies similar efficiencies for their separation and column recovery, as well as graphite furnace sensitivities. 

Fig. 4.10 Calibration curves for ICSn (R=butyl, phenyl, c-hexyl) separated by HPLC-GFAA with strong cation exchange (SCX) columns using Me0H/H20/NH40Ac eluents are shown with respective correlation...

R butyl, phenyl, hexyl R butyl, phenyl, methyl... 

A cationic catalyst prepared from [Rh(R-(PhCH2)MePhP)2(nbd)]+C104 has been used to hydrosilylate several alkylphenylketones (43). Optical yields ranging from 5 to 62% were reported, the most impressive being those for acetophenone (31.6% ee), ethyl phenyl ketone (43.1% ee), and r-butyl phenyl ketone... 

Enantioselective Hydrosilylation of C=N Double Bonds in Ketoximes and Ketimines. Homogeneous enantioselective hydrosilylation of prochiral alkyl aryl ketoximes has been carried out by using a Rh-(R,R)-NORPHOS catalyst. Thus, hydrosilylation of r-butyl phenyl ketoxime in the presence of [Rh(COD)Cl]2-(R,R)-NORPHOS followed by aqueous acidic work-up afforded the corresponding amine (eq 3) [16.5% ee, (5)], which became inverted to 15.0% ee (R) when this reaction was performed in the presence of added ammonium hexafluo-rophosphate (RhiNHaPF = 1.1, CH2CI2 solvent). ... 

Asymmetric borohydride reduction. Colonna and Fornasier have examined the reduction of ketones with sodium borohydride under phase-transfer conditions in the presence of optically active ammonium salts containing at least one hydroxyl group. Of the seven catalysts tested (-)-benzylquininium chloride (1) (7, 311) was the most effective for asymmetric reduction of r-butyl phenyl ketone (pivalo-phenone) to the corresponding carbinol with optical yields as high as 32%. Two factors would appear to be important for this asymmetric reduction the catalyst must be conformationally rigid and the hydroxyl group must be in the 8-position to the onium function. ... 

Borohydride reduction of ketones. The reduction of ketones to alcohols by sodium borohydride in benzene-water has been reported to be catalyzed by this salt (6, 249). However, no asymmetric induction was noted in the case of 2-octanone, 1-phenyl-1-propanone, or acetophenone. More recently, asymmetric induction has been observed with more hindered ketones. The maximum was observed with r-butyl phenyl ketone when an enantiomeric excess of 14% of the (R)-alcohol could be obtained. The enantiomeric excess is only 3.6% in the reduction of isopropyl phenyl ketone. No asymmetric induction was observed when ( —)(R)-N,N-dimethyl-N-dodecylamphetaminium bromide was used as catalyst. The structure of the chiral catalyst is evidently important. ... 

It is known that cydodextrins have a hydrophobic cavity (a binding site for aromatics) and a hydrophilic external surface. A template-directed asymmetric sulfoxidation has been attempted with various aryl alkyl sulfides. [91]. Oxidations were performed by using metachlo-roperbenzoic add in water in the presence of an excess of p-cyclodextrin. The best ee (33%) was attained for mem-(r-butyl)phenyl ethyl sulfoxide. The decrease in the amount of P-cyclodex-trin below 1 mol equiv. causes a sharp decrease in enantioselectivity because of competition with oxidation of free substrate by the oxidant. Similarly, Drabowicz and Mikolajczyk observed modest asymmetric induction (27% ee) in the oxidation of Ph-S-n-Bu with H2O2 in the presence of P-cyclodextrin [92]. 

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